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LTE Broadcast for TV distribution

July 02 2014

We believe LTE will play a major role in TV distribution in the near future. LTE can give service providers the flexibility to alter between broadcast and unicast, depending on how many people want to watch at a particular time. This way, they can offer consumers personalized mobile TV with good quality in an efficient way.

Ericsson’s latest Mobility Report predicts that by 2019, the annual video traffic in mobile networks will grow by around 55 percent, as consumer’s desire for “TV Anywhere” and “TV Anytime” is at an all-time high. On the other hand, terrestrial TV, is rapidly losing market share to Direct-To-Home (DTH) TV, Cable and fixed BB.

Terrestrial TV is today delivered by means of broadcasting, whereas Mobile TV and other mobile video is delivered via cellular networks using unicasting where each user is served by a separate video stream. Broadcasting a TV program is more spectrally efficient than unicasting only if the number of receivers simultaneously interested in a TV program exceeds a threshold within a geographic area. For Germany, the threshold is a viewing share of about 1-4%, calculated for a dense urban area. There are only about 10 programs, within an average yearly viewing share, above this threshold [1]. This means that nowadays, continuous broadcasting in a cellular deployment appears to be efficient only for a small part of TV content. In the case of dynamic, on-demand broadcasting, the number of broadcast streams at any point in time can be even lower. Therefore, a flexible system, such as LTE, is essential.

Overview of LTE Broadcast

LTE Broadcast is an integral part of a mobile communication infrastructure, which is built to support broadcast and unicast communication. With LTE Broadcast, the same system is capable of establishing communication channels for interactivity as well as unidirectional broadcast channels. If there is only low interest in a certain part of the network, the infrastructure can stop the broadcast and reuse the resources for unicast communication. The system is highly adaptive and uses broadcast only during times and in areas where the interest in the content is sufficiently high. Ericsson is convinced that such flexibility is key for efficient TV distribution.

Support for Multimedia Broadcast/Multicast Service (MBMS) has been standardized by 3GPP. MBMS for LTE was standardized in 3GPP Release 9 and is often called eMBMS. eMBMS traffic is time multiplexed with unicast traffic, which can be used to enable interactivity for broadcast services or upcoming “Hybrid-Digital-TV” services.

Content can be protected on the application layer using standardized encryption methods. Conversely, as eMBMS does not make use of the LTE specific ciphering, it is possible to receive LTE Broadcast services without having a SIM card if the device supports this. This facilitates anonymous and free-to-air reception.

We believe that an optimal LTE Broadcast solution for video distribution addressing all layers is to combine eMBMS with DASH (Dynamic Adaptive Streaming using HTTP) and HEVC (High Efficiency Video Codec, ITU-T H.265).

eMBMS, in a multi-cell deployment, uses a single-frequency network (SFN) configuration, establishing a so called MBSFN. Cells in an MBSFN area have to be tightly time synchronized. The signal parameters are suitable for cellular MBSFN operation. However, in order to be able to use eMBMS for an MBSFN from existing High Power High Tower, (HPHT) TV stations new transmit signal variants would be required, which would have to be standardized. Unfortunately, these signals are inherently more difficult to receive by mobile receivers.

Another issue of TV stations is their large separation distance together with regulatory transmit power limitation, which results in low received signal strength for mobile receivers without external antenna, in particular indoors. A likely consequence would be that HPHT transmission continues to focus on stationary reception with external antennas. Ericsson Research has together with Qualcomm outlined LTE based solutions as part of a joint proposal to the call for proposals for the ATSC3.0 standard. In North America the ATSC (Advanced Television Standardization Committee) is working on a next generation TV broadcasting standard. Currently discussions are ongoing on the scenarios that are typical for mobile and portable broadcast reception.

LTE Broadcast Cologne study

To illustrate the use of LTE broadcast we have analyzed the service reception probability for TV broadcasting using eMBMS [1]. For this purpose the site of one of the existing 3G networks around Cologne, Germany, have been assumed to be upgraded to LTE, including eMBMS. In this example, we have used a transmission mode for eMBMS that yields similar spectral efficiency (2.8b/s/Hz) as DVB-T2 as currently being discussed for Germany. Figure X shows a map of the area with the polygons served by each site colored according to the service probability, assuming indoor reception. In the center 10 km radius where most of the population lives, the service probability from all sites is above 95%. In the ring between 10 km and 20 km the probability decreases, network density is smaller here, but still 93% of the sites provide service probability better than 95%.

LTE Broadcast coverage map using a transmission mode to achieve a similar spectral efficiency as DVB-T2 as being considered for Germany.